1. Field of the Invention
The present invention involves methods for controlling fluid flow between fluid inlets and chambers, and more particularly, a method for controlling such flow to or from a pressure/vacuum chamber.
2. Description of the Prior Art
Ethylene oxide gas sterilization processes include preconditioning and exhaust phases wherein a vacuum is drawn in the sterilization chamber and a sterilizing phase wherein the goods within the chamber are exposed to ethylene oxide gas, or a mixture of ethylene oxide and freon under pressure. To provide relief from the vacuum drawn during the process, chambers are equipped with atmospheric vents. The vent must, of course, be sealed during conditions of vacuum and pressure within the chamber. During the vacuum phases, a faulty seal effects cycle efficiency and during the pressure phase, a faulty seal permits gas leakage through the vent line and into the area surrounding the chamber and thus, poses a serious safety hazard.
The conventional method of sealing chambers in which a process including controlled alternating vacuum and pressure conditions is practiced, is by providing a solenoid valve in the vent line to seal for vacuum. The solenoid valves also relieve the vacuum at predetermined electronically controlled times. The solenoid valves do not seal against both vacuum and pressure conditions, so a one-way check valve must also be placed in the vent line to seal against pressure leaks. Both the check valves and the solenoid valves, however, often present quality and reliability problems.
There are commercially available direct acting solenoid valves which can be installed back to back in opposite directions to provide sufficient flow to relieve the vacuum in smaller sterilizers. However, the use of these valves does not provide adequate flow to relieve vacuum at acceptable rates in larger units. To do so apparently requires too much electrical power and greater mass in the coil, making their use economically unfeasible for sterilization equipment.
There is a need for a method of controlling fluid flow from a fluid inlet to a chamber which permits adequate flow to relieve a vacuum in the chamber at an acceptable rate. There is a further need, especially in processes such as ethylene oxide gas sterilization, for a method of controlling fluid flow from the chamber through the inlet to atmosphere. Finally, there is a need for such a method which is economically feasible and reliable regardless of the size of the chamber.